Based on what you're describing, it sounds like your A/F Sensor (Air Filter Ratio Sensor) is bad. The A/F sensor is similar to an O2 sensor in task but the A/F sensor detects a wider air/fuel ratio range than the O2 sensor, commonly found in newer model vehicles. Since you are having trouble starting up in the morning, my assumption is that your A/F sensor is bad, causing your 4Runner to not properly get up to temperature upon start up. The other assumption is that your coolant system error (P0125) is a direct result from the A/F sensor being bad. If your 4Runner can't get up to proper start temperature, it will cause your coolant system to malfunction.
I would replace your A/F sensor and see if your 4Runner throws either code again. I think these run around $200. If you want to be 100% sure, pull the sensor and run an ohm meter on it. I'm not 100% sure what the required resistance is, I'll try to do some research and post it for you.
Matt
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by: Michael-BestPosted on 2009-07-04 at 07:44:25ID: 24777031
Best take it to an expert to check it & repair it.
Less time & money wasted the better?